1. Field of the Invention
The present invention is directed to an etalon, a wavelength monitor/locker using the etalon, more particularly to an integrated wavelength locker which can be placed in an optical path of an application beam or in an optical path of a monitor beam.
2. Description of Related Art
Some radiation sources exhibit wavelength drift over time in excess of that tolerable for many applications. For many applications, the wavelength stability is required to be within 0.05 nm from a desired wavelength. This drift becomes increasingly important as the lifetimes over which these radiation sources are to be deployed increases. Factors such as temperature, age, operating power level, etc., all effect the output wavelength. By monitoring at least one of the direction of the wavelength change, the degree of the change and the percentage of the light being radiated at the different wavelengths, any or all factors which may be causing this change can be modified in accordance with the monitored signal via a feedback loop to stabilize the wavelength of the radiation source. Preferably, both the power and the wavelength are monitored. The wavelength may be controlled by altering a temperature of the light source, e.g., by a thermally cooled unit, and the power may be controlled in accordance with the injection current. Since the power and the wavelength are interdependent, i.e., a change in one parameter affects the other, the best stability is achieved when both are controlled.
Such monitoring and stabilizing systems typically involve using a unit which is external to the radiation source itself. Such external units include crystal gratings, fiber gratings, spectrometers, and Fabry-Perot etalons, both straight and inclined. The grating systems include relatively large control units external to the radiation source. While etalon-based systems offer a more compact solution, so far these etalons are still separate units which may become improperly aligned, either with photodetectors or with optical elements required to direct and control the light onto the photodetectors.
The present invention is therefore directed to an etalon and a wavelength monitor/locker which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
At least one of these and other objectives may be realized by providing a wavelength locker including a divider creating at least a first beam and a second beam from an input beam from a light source, a first photodetector receiving the first beam, a second photodetector receiving the second beam, a substrate including an etalon in a path between the divider and the first photodetector, and another element performing an optical function, and a connector supplying outputs of the monitor photodetector and the reference photodetector to a wavelength controller of the light source.
The divider may include a diffractive grating for deflecting a portion of the input beam into higher orders. The diffractive grating may be polarization insensitive.
The wavelength locker may include an optics block which directs the first and second beams to the first photodiode and the second photodiode, respectively. The divider may be integrated on the optics block. The optics block may provide at least one of collimating and focusing to at least one of the input beam, the first beam and the second beam.
At least two of the etalon, the divider and the optics block may be bonded together on a wafer level and diced to form that portion of the wavelength locker.
The first photodetector and the second photodetector may be mounted on a substrate. The substrate may have a hole therein between the first photodetector and the second photodetector. The substrate may have a transparent region therein between the first photodetector and the second photodetector. A spacer may be provided between the substrate and the etalon. The substrate may have a recess therein in which the first photodetector and the second photodetector are mounted. The another element performing an optical function may be at least one of a refractive element and a diffractive element. The optics block may reflect the first and second beams to the first photodetector and the second photodetector, respectively. The optics block provides multiple reflections to the first and second beams to direct them to the first photodetector and the second photodetector, respectively. The another element performing an optical function may be another etalon in a path between the divider and the second photodetector, the another etalon having a different path length than the etalon between the divider and the first photodetector. The another element performing an optical function may be the divider.
The etalon may be solid or have a gap between opposing reflective portions thereof. The divider may output a third beam as an application beam to be directed to further applications.
The above and other objects may be realized by providing a method of designing a polarization insensitive grating including starting with a design of a grating providing a desired ratio of diffracted light to undiffracted light for unpolarized light, first varying one of an etch depth and a duty cycle until the desired ratio is realized for light of a first polarization, second varying another of the etch depth and duty cycle until the desired ratio is realized for light of a second polarization, orthogonal to the first polarization, and performing the first and second varying until a ratio for the first polarization is in sufficient agreement with a ratio for the second polarization. The method first varying may alter the duty cycle and the second varying may alter the etch depth.
The above and other objects may be realized by providing a wavelength monitor including a first substrate being optically transparent and having first and second opposing faces, at least two photodetectors, an etalon in the path of at least one of the at least two photodetectors, the etalon and the first substrate being bonded together, wherein all elements needed to create at least two beams from an input beam, each of the at least two light beams being incident on a respective photodetector, and to direct each of the at least two beams to the respective photodetector, are on at least one of the first substrate and any structure bonded to at least one of the first substrate and the etalon.
The above and other objects may be realized by providing an etalon including a continuous substrate which is to extend across at least two photodetector, at least two opposing reflective portions on the substrate in a path of at least one of the at least two photodetectors, with at least one of the at least two photodetectors not having reflective portions in a path thereof. The continuous substrate may include two continuous substrates and a spacer bonded to the two continuous substrates, forming a gap between the two continuous substrates, the at least two opposing reflective portions being on opposing faces of the two continuous substrates. The at least two opposing reflective portions may be formed on continuous wafer which is diced to form the continuous substrate.
The above and other objects may be realized by providing an etalon block including a substrate having opposing reflective portions serving as an etalon in a portion thereof and another element performing another optical function. The etalon block may further include an optics block adjacent to the substrate, at least one of the optics block and the substrate including a divider for creating at least a first beam and a second beam from an input beam from a light source, the first beam passing through the etalon and at least one of the second beam and the input beam passing through the other optical element. The other optical element may be another etalon, separate from the etalon, the second beam passing through the another etalon, the another etalon having a different optical path length than the etalon. The other optical element may be a divider for creating at least a first beam and a second beam from an input beam from a light source.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.